There are known many methods for producing a 1,3-disubstituted pyrazole-4-carboxylic acid ester by reaction of a 2-alkoxymethyleneacylacetate, in which an alkoxy group acts as a leaving group, with a hydrazine (see e.g. Patent Documents 1 to 3). For instance, Patent Document 3 discloses that an isomer mixture of ethyl 3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylate and ethyl 5-(difluoromethyl)-1-methyl-1H-pyrazole-4 carboxylate can be obtained from an aqueous solution of ethyl 2-ethoxymethylene-4,4-difluoroacetoacetate and methylhydrazine.
On the other hand, there have been proposed methods for producing a 1,3-disubstituted pyrazole-4-carboxylic acid ester by reaction of a reaction substrate in which an amino group acts as a leaving group. For instance, Patent Document 4 discloses that a 3-perhalo-substituted pyrazole can be obtained by reaction of a 2-perhaloacyl-3-aminoacrylic acid derivative with a hydrazine. Patent Document 5 discloses that a 89.2:10.8 mixture of ethyl 3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylate and its isomer (ethyl 5-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylate) can be obtained by reaction of ethyl 2-(difluoroacetyl)-3-(dimethylamino)acrylate with methylhydrazine.